If there was any lingering doubt that Mayor Bill de Blasio’s mostly harmonious relationship with the City Council was about to change, Councilman Ritchie Torres may put that question to rest.

Mr. Torres, a Democrat from the Bronx, has been chosen by the Council’s newly selected speaker, Corey D. Johnson, to be in charge of a new investigations unit that will look into the operation of city agencies.

In an interview, Mr. Torres said that between 10 and 15 professional investigators, possibly including former prosecutors, would be hired and that the committee would use them to conduct its own inquiries.

Among the areas of possible investigative interest, according to Mr. Torres: “The abuse of placards. The use of eminent domain. The disposition of public land. Deed restriction. The disbursement of city subsidies,” he said. “All of it is on the table.”

In general, oversight hearings conducted by the Council in recent years have been in response to issues raised by the Department of Investigations, the city’s comptroller, the press or outside groups, not the fruits of its own discoveries.

“The message here is that it’s a new day in City Council oversight,” Mr. Torres, 29, said. “Newton’s first law of motion applies to the physics of government. An object will remain at rest unless acted upon by an outside force.”

He said he viewed his new role, which is expected to be formally announced Thursday along with other Council committee assignments for the next four years, as focused on prodding a “complacent bureaucracy” to better provide city services and dig “deep into the operational failures of city government.”

The unit is to be housed in the Council’s oversight and investigations committee, with Mr. Torres as the new committee chairman. It could become the most prominent nexus for public clashes between the Council and the mayor, which have been rare during the mayor’s first term. No legislation passed by the Council received a mayoral veto, indicating that none came up for a vote without his support.

“It will be a challenge for City Hall,” said Peter Madonia, the former chief operating officer for The Rockefeller Foundation who served as chief of staff to Mayor Michael R. Bloomberg and as an informal adviser to Mr. de Blasio. But, he added, it could also provide a chance for the Council and the mayor to work together on improving agency performance — with one caveat.

“The politics gets in the way of that sometimes,” he said.

Eric F. Phillips, the mayor’s press secretary, offered a short response when asked about the creation of the new unit. “The Council already holds hearings and scrutinizes the work of agencies,” he said.

Mr. Johnson said in an interview last week that it was his intention to reconstitute an investigations unit for the Council of the sort first created in the 1980s under the city’s first Council speaker, Peter Vallone Sr. The goal, at the time, was to assert the Council’s independence from the mayor, much as Mr. Johnson said he envisioned its work this time around.

Mr. Torres, who conducted a courtroom-like examination of the New York City Housing Authority’s handling of lead paint at a public hearing last year, said he would seek to partner with other oversight entities in city government, such as the Department of Investigation and the city’s comptroller. He cited his “deep working relationship” with Mark Peters, the commissioner of the Department of Investigation.

Mr. Peters, in a telephone interview, said he had not discussed details of the new unit with the Council, but was “pleased that there’s a real expressed interest in making a more vigorous use of the investigations that D.O.I. does.”

The Council’s rules committee is expected to vote Thursday on Mr. Torres’s committee assignment, along with others.

Among the most prominent, the powerful land use committee is expected to be run by Councilman Rafael Salamanca Jr. of the Bronx and the finance committee is expected to be lead by Councilman Daniel Dromm of Queens, according to a person familiar with the discussions who was not authorized to announce them before Thursday. Laurie Cumbo, a Brooklyn councilwoman, is expected to be named majority leader for the Council’s Democrats, who outnumber Republicans, 47 to 4.

A version of this article appears in print on , on Page A22 of the New York edition with the headline: City Council Opens Investigative Unit. Order Reprints | Today’s Paper | Subscribe